/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package com.vip.vjtools.vjkit.concurrent.jsr166e;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.concurrent.atomic.AtomicLong;

/**
 * 移植
 * http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/LongAdder.java Revision.1.17
 * 
 * One or more variables that together maintain an initially zero
 * {@code long} sum.  When updates (method {@link #add}) are contended
 * across threads, the set of variables may grow dynamically to reduce
 * contention. Method {@link #sum} (or, equivalently, {@link
 * #longValue}) returns the current total combined across the
 * variables maintaining the sum.
 *
 * <p>This class is usually preferable to {@link AtomicLong} when
 * multiple threads update a common sum that is used for purposes such
 * as collecting statistics, not for fine-grained synchronization
 * control.  Under low update contention, the two classes have similar
 * characteristics. But under high contention, expected throughput of
 * this class is significantly higher, at the expense of higher space
 * consumption.
 *
 * <p>This class extends {@link Number}, but does <em>not</em> define
 * methods such as {@code equals}, {@code hashCode} and {@code
 * compareTo} because instances are expected to be mutated, and so are
 * not useful as collection keys.
 *
 * <p><em>jsr166e note: This class is targeted to be placed in
 * java.util.concurrent.atomic.</em>
 *
 * @since 1.8
 * @author Doug Lea
 */
public class LongAdder extends Striped64 implements Serializable {
	private static final long serialVersionUID = 7249069246863182397L;

	/**
	 * Version of plus for use in retryUpdate
	 */
	final long fn(long v, long x) {
		return v + x;
	}

	/**
	 * Creates a new adder with initial sum of zero.
	 */
	public LongAdder() {
		// empty
	}

	/**
	 * Adds the given value.
	 *
	 * @param x the value to add
	 */
	public void add(long x) {
		Cell[] as;
		long b, v;
		int[] hc;
		Cell a;
		int n;
		if ((as = cells) != null || !casBase(b = base, b + x)) {
			boolean uncontended = true;
			if ((hc = threadHashCode.get()) == null || as == null || (n = as.length) < 1
					|| (a = as[(n - 1) & hc[0]]) == null || !(uncontended = a.cas(v = a.value, v + x)))
				retryUpdate(x, hc, uncontended);
		}
	}

	/**
	 * Equivalent to {@code add(1)}.
	 */
	public void increment() {
		add(1L);
	}

	/**
	 * Equivalent to {@code add(-1)}.
	 */
	public void decrement() {
		add(-1L);
	}

	/**
	 * Returns the current sum.  The returned value is <em>NOT</em> an
	 * atomic snapshot; invocation in the absence of concurrent
	 * updates returns an accurate result, but concurrent updates that
	 * occur while the sum is being calculated might not be
	 * incorporated.
	 *
	 * @return the sum
	 */
	public long sum() {
		long sum = base;
		Cell[] as = cells;
		if (as != null) {
			int n = as.length;
			for (int i = 0; i < n; ++i) {
				Cell a = as[i];
				if (a != null) sum += a.value;
			}
		}
		return sum;
	}

	/**
	 * Resets variables maintaining the sum to zero.  This method may
	 * be a useful alternative to creating a new adder, but is only
	 * effective if there are no concurrent updates.  Because this
	 * method is intrinsically racy, it should only be used when it is
	 * known that no threads are concurrently updating.
	 */
	public void reset() {
		internalReset(0L);
	}

	/**
	 * Equivalent in effect to {@link #sum} followed by {@link
	 * #reset}. This method may apply for example during quiescent
	 * points between multithreaded computations.  If there are
	 * updates concurrent with this method, the returned value is
	 * <em>not</em> guaranteed to be the final value occurring before
	 * the reset.
	 *
	 * @return the sum
	 */
	public long sumThenReset() {
		long sum = base;
		Cell[] as = cells;
		base = 0L;
		if (as != null) {
			int n = as.length;
			for (int i = 0; i < n; ++i) {
				Cell a = as[i];
				if (a != null) {
					sum += a.value;
					a.value = 0L;
				}
			}
		}
		return sum;
	}

	/**
	 * Returns the String representation of the {@link #sum}.
	 * @return the String representation of the {@link #sum}
	 */
	public String toString() {
		return Long.toString(sum());
	}

	/**
	 * Equivalent to {@link #sum}.
	 *
	 * @return the sum
	 */
	public long longValue() {
		return sum();
	}

	/**
	 * Returns the {@link #sum} as an {@code int} after a narrowing
	 * primitive conversion.
	 */
	public int intValue() {
		return (int) sum();
	}

	/**
	 * Returns the {@link #sum} as a {@code float}
	 * after a widening primitive conversion.
	 */
	public float floatValue() {
		return (float) sum();
	}

	/**
	 * Returns the {@link #sum} as a {@code double} after a widening
	 * primitive conversion.
	 */
	public double doubleValue() {
		return (double) sum();
	}

	private void writeObject(ObjectOutputStream s) throws IOException {
		s.defaultWriteObject();
		s.writeLong(sum());
	}

	private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException {
		s.defaultReadObject();
		busy = 0;
		cells = null;
		base = s.readLong();
	}

}
